1. Field of the Invention
The present invention relates to a storage-stable solution of carbonated magnesium methoxide of the formula Mg(CH.sub.3 O).sub.2 (CO.sub.2).sub.n in methanol, a process for the preparation of a storage-stable solution of carbonated magnesium methoxide of the formula Mg(CH.sub.3 O).sub.2 (CO.sub.2).sub.n in methanol by reacting metallic magnesium with methanol and CO.sub.2, and to a process for the preparation of a storage-stable solution of carbonated magnesium methoxide of the formula Mg(CH.sub.3 O).sub.2 (CO.sub.2).sub.n in methanol by reacting magnesium methoxide in methanol with CO.sub.2. The present invention also relates to a method of preserving paper and a method of preparing a catalyst for the polymerization of olefins using a storage-stable solution of carbonated magnesium methoxide in methanol.
2. Discussion of the Background
Magnesium alcoholates (or alkoxides) are, as a rule, not very soluble in the corresponding alcohols. In some cases, magnesium alcoholates are virtually insoluble in the corresponding alcohols. An exception is magnesium methoxide, which has a solubility of up to about 12% by weight in methanol.
A technically simple method for increasing the solubility of magnesium alcoholates is carbonation. Gaseous, liquid or solid CO.sub.2 is introduced into a suspension of the magnesium alcoholate in the corresponding alcohol. A soluble CO.sub.2 adduct forms. In the case of magnesium ethoxide, the CO.sub.2 adduct is soluble up to a concentration of more than 30% by weight in ethanol, whereas pure magnesium ethoxide is virtually insoluble in ethanol.
Alcohol-soluble carbonated magnesium alkoxides are widely used. Thus, for example, magnesium alkoxides brought into solution by carbonation can be used in the long-term preservation of paper, in particular books, and can be substituted for the zinc alkyls which are likewise used for this purpose according to U.S. Pat. No. 3,969,549, EP-A 0,285,227, U.S. Pat. No. 4,318,963 and U.S. Pat. No. 3,939,091, but which present problems during use.
According to European Patent 0,159,150 and European Patent 0,236,082, a further field of use is the preparation of catalysts for the polymerization of olefins. For example, spherical magnesium methoxide and magnesium ethoxide are useful for this purpose. Spherical magnesium methoxide and magnesium ethoxide can be prepared, for example, by spray drying or precipitation of carbonated magnesium methoxide solutions or magnesium ethoxide solutions, and, if required, subsequent decarbonation.
It is known in principle that solutions of carbonated magnesium alcoholates can be prepared according to the two reaction schemes below. On the one hand, metallic magnesium can be reacted with an alcohol ROH and CO.sub.2 (equation (1)). On the other hand, a magnesium alkoxide can be reacted with CO.sub.2 (equation (2)): EQU Mg+2 ROH+n CO.sub.2 .fwdarw.Mg (OR).sub.2 (CO.sub.2).sub.n +H.sub.2( 1) EQU Mg(OR).sub.2 +n CO.sub.2 .fwdarw.Mg(OR).sub.2 (CO.sub.2).sub.n( 2)
Here, R denotes an alkyl group, preferably a branched or linear C.sub.1 -C.sub.4 alkyl group.
European Patent 0,236,082 teaches the preparation of carbonated magnesium alkoxides by reacting magnesium alkoxides with CO.sub.2 in a solvent. Preferred solvents are alcohols. For example, the preparation of carbonated magnesium ethoxide by reacting magnesium ethoxide with CO.sub.2 in ethanol as a solvent is disclosed.
In "Reagents for Organic Synthesis" vol. 1 page 631, Fieser et al describe the preparation of carbonated magnesium methoxide by two different routes. In one procedure, a suspension of magnesium methoxide in methanol is reacted with CO.sub.2. In the other, magnesium turnings are reacted with methanol to give magnesium methoxide. After the methanol has been partially stripped off at 50.degree. C. and reduced pressure, dimethylformamide is added as a solvent and CO.sub.2 is passed into this solution. The remaining methanol is distilled off, and a slightly yellow solution of carbonated magnesium methoxide in dimethylformamide is obtained.
European Patent 0,159,150 reports on the use of solutions of carbonated magnesium alcoholates in alcohols for the preparation of active catalyst carriers for olefin polymerization. The solutions used contain 10 to 80% by weight of magnesium alcoholate, and 0.1 to 4 mol of CO.sub.2 per mol of magnesium and are prepared by reacting magnesium alcoholate, dispersed in alcohol, with gaseous CO.sub.2.
However, the alcoholic solutions of carbonated magnesium alkoxides according to these references must be used within a short period of time, since discoloration, precipitation and gel formation can occur after only a few days, even on storage in tightly sealed vessels.
The industrial use of such solutions is considerably limited. On the one hand, colored solutions cannot be used, for example, for the long-term preservation of books. On the other hand, solutions in which there is a danger of uncontrolled precipitation cannot be used for the preparation of catalysts based on magnesium alkoxide.